In machining of metals and other materials, there are many applications where it is desirable to make a hole and thread it with a single tool. The single tool for hole making and threading is needed not only for through holes but also for blind holes in a workpiece. The advantage of such a tool is that it reduces the number of motions or operations required to produce a threaded hole; it is especially advantageous in conjunction with high speed machining operations.
In the prior art, it is known to use a single tool for drilling a hole and forming internal threads by swaging or coining the metal. A tool of this kind is disclosed in the Barth U.S. Pat. No. 2,703,419 granted Mar. 8, 1955 which describes a swaging tap having a drill or end mill on the leading end thereof to cut the hole which is to be threaded. This tool is rotated and the hole is cut and threaded on the inward feed of the tool and the tool is unscrewed from the threaded hole. A similar tool is disclosed in the Grenell U.S. Pat. No. 4,271,554 granted June 9, 1981. In tools of this kind, the maximum diameter of the swaging tap must be larger than the maximum diameter of the drill or end mill. Further, as described in the Grenell patent, the minor diameter of the female threads is smaller than the diameter of the drilled hole and the major diameter of the threads is larger than the diameter of the drilled hole.
A general object of this invention is to provide a combined hole making and threading tool which may be used for both through holes and blind holes and which lends itself to high speed machining.